Capacitor charge and discharge circuit for stroboscopes



July 25, 1950 n. D. KNOWLES EI'AL 26 CAPACITOR CHARGE AND DISCHARGECIRCUIT FOR S'I'ROBOSCOPES Original Filed May 17, 1935 2 Sheets-Sheet 1Ma er- 33 Qac Illa far- WITNESSES: D I/tJ/ENTORS c ewey D. now/e5 3 2?and Cecil 1 Hal/er.

firm/L BY 960- I A'ITORNE D. D. K CAPACITOR CHARGE AND DISCHARGE CIRCUITFOR STROBOSCOPES Original Filed May 17, 1935 2 Sheets-Sheet 2 l arlbb/efFquency WITNESSES: I INVENTORS r Dewey Z7. mow/es and 6B l /5Ha //f" cI. I

A'ITOR Y Patented July 25, 1950 CAPACITOR CHARGE AND DISCHARGE CIRCUITFOR STROBOSCOPES Dewey D. Knowles, Verona, N. J., and Cecil'E.

Haller, Lititz, Pa., assignors to Westinghouse Electric Corporation,East Pittsburgh, Pa., a corporation of Pennsylvania ApplicationSeptember 17, 1941, Serial No. 411,134,

now abandoned, which is a division of application Serial No. 120,940,January 16, 1937, now Patent No. 2,310,092, dated February 2, 1943,which in turn is a division of application Serial No. 22,012, May 17,1935, now Patent No. 2,085,100, dated June 29, 1937. Divided and thisapplication August 30, 1946, Serial No.

1 Claim.

Our invention relates to electric discharge apparatus and it hasparticular relation to the control of electric discharge devices of thetype having a discharge initiating electrode, but not a dischargemaintaining electrode such as a keepalive.

This application is a division of our application Serial No. 411,134,filed September 17, 1941, now abandoned; which is in turn a division ofour application Serial No. 120,940, filed January 16, 1937 which hasbecome Patent No. 2,310,092 issued Feb. 2, 1943; which is in turn adivision of our application Serial No. 22,012, filed May 17, 1935 whichhas become Patent No. 2,085,100 issued June 29, 1937.

It is an object of our invention to provide a circuit for controllingthe initiation. and extinction of the discharge in a discharge device ofthe mercury pool type that is equipped with a discharge initiatingelectrode.

Another object of our invention is to provide apparatus for periodicallyenergizing a discharge device of the mercury pool type that is equippedwith a discharge initiating electrode,

A further object of our invention is to provide apparatus for energizingand deenergizing, with variable periodicity, a discharge device of thetype that is normally completely deenergized.

More specifically stated, it is an object of our invention to provideapparatus for energizing and deenergizing, with precisely determinableperiodicity, a discharge device of the type that is equipped with adischarge starting electrode, but not with a discharge maintainingelectrode.

In the following discussion and in the claim, we shall refer to adischarge device having a plurality of principal electrodes and aplurality or pair of starting electrodes. Such an expression is drawnwith the thought in mind that it shall denominate a discharge devicehaving at least four electrodes, 1. e., separate pairs of principal andstarting electrodes.

In the preferred structure of the discharge device utilized in thepractice of our invention, however, only three electrodes are utilized;an anode, a mercury pool cathode and a starting electrode, preferablycomposed of boron carbide or silicon carbide, a portion of which isimmersed in the mercury. The mercury pool thus serves the doublefunction of cathode and starting electrode cooperative witha boron orsilicon carbide electrode. The use of the mercury in the double capacityis, of course, in th interest of economy and convenience and should innoway limit the tance from the pool and in initiating th discharge aspark may be ignited between the starting electrode and the pool.Moreover, the starting electrode may be a band surrounding the envelopeof the discharge device in the region of the pool. It is to be noted,however, that while discharges of the latter types may be utilized,they. offer diliculties when used for stroboscopic pur poses. To ignitesuch discharge devices considerable and persistent starting potential isrequired and as far as we are aware, the operation of such is uncertain.However, it

discharge devices should b kept in mind that while the discharge devicesof the type incorporating the silicon or boron carbide startingelectrode are preferable for stroboscopic work, where the dischargedevices of the last-mentioned types have utility and where the teachingof our invention is otherwise fol-- lowed such use of the dischargedevices are equivalent which fall within the scope of our invention. 1

In accordance with our invention, a source of electrical energy isconnected across the principal electlodes'of the discharge device and acapacitor is connected in parallel with the principal elec In thecircuit ofthe starting electrodes of the discharge device a valve isconnected:

trodes.

The supply of starting current through the valve and the rate of chargeand discharge *of the capacitor are so timed that the dischargedevicelarity in the appended claim. The invention ,it-

self, however, both as to its organization and its method of operation,together with additional objects and advantages thereof, will best beunderstood from the following description of specific embodiments whenread in connection with the accompanying drawings, in which:

Figure l is a diagrammatic view showing an embodiment of our invention;

Fig. 2 is a diagrammatic view showing a modification of our invention;

Fig. 3 is a graph illustrating the operation of the apparatus shown inFig. 2;

Fig. 4 is a diagrammatic view showing a further modification of ourinvention;

Fig. 5 is a diagrammatic view showing a still further modification ofour invention; and

Fig. 6 is a graph illustrating the operation of the apparatus shown inFig. 5.

Our invention is illustrated herein as utilized in a stroboscope. Forstroboscopic purposes, a luminous discharge which can be ignited andextinguished with a precise periodicity is a desideratum. However, aswill be manifest from the following description, our invention. may alsobe utilized for other purposes.

The apparatus shown in Fig. 1 comprises a discharge device I having ananode 3, a mercury pool cathode 5, and a starting electrode I composedof a high resistive material such as boron carbide or silicon carbide, aportion of which is immersed in the mercury 5. When the discharge deviceI is energized, as shall be explained hereinafter, the radiationsemitted by the luminous spot formed on the mercury pool surface areprojected on the body 9 under observation which is illustrated as thespoke of a rotating wheel II. The discharge device I is energized anddeenergized at a periodicity corresponding to the periodicity of thewheel II and when the spoke 9- is observed in the illumination emittedby spot, it appears to be at rest. When we refer hereinafter to anelectrode or a material of the igniter type we mean thereby an electrodesuch as I or the material of which it is formed. The

material in question may be not only Of silicon carbide or boron carbidebut any other substance which when contacting an electrode and operatedby current has the property of facilitating the initiation of an arebetween said electrode and another electrode.

A capacitor I3 is connected to the anode 3 of the discharge device. Ithrough an inductor I5 and directly to the cathode 5 of the dischargedevice. The capacitor I3 is charged through a resistor I1 from a sourceI9 which is preferably of the direct current type. The startingelectrode I is connected to the capacitor [3 through an auxiliarydischarge device 2| and the inductor I5. The auxiliary discharge device2| is preferably of the type having an abrupt characteristic. It is.provided with an anode 23, a hot cathode and a control electrode 21which are immersed in a gaseous medium. The anode 23 is connected to theinductor I5 while the cathode 25 is connected to the starting electrode1 through a current limiting resistor 29. The control electrode 21. isconnected to the cathode 25 through a variablebiasing battery- 3 I Inoperation, the auxiliary discharge device 2I is normally deenergized.The capacitor I3 is charged through the resistor II in series therewith.When it attains a difference of potential predetermined by the magnitudeof the bias in the control circuit of the auxiliary discharge device thelatter is energized and a pulse of current is transmitted between thestarting electrode I and the mercury pool 5. A discharge is, therefore,initiated between the principal electrodes 3 and 5 of the main dischargedevice I which persists for an interval of time predetermined by therelative magnitudes of the inductor I5 and the capacitor I3. Thecapacitor I3 is discharged when the main discharge device I is energizedand when the main discharge device is extinguished, the capacitor isrecharged and the above-described process is repeated. Since theelectrode I and the mercury 5 both cooperate to produce an arc, they maybe designated together as a plurality of starting electrodes.

The excitation of the main discharge device I is periodic. Theperiodicity of the excitation may be varied either by varying theresistor II in series with the capacitor I3, and thus varying the rateof charging of the capacitor, or by varying the biasing battery in thecontrol circuit of the auxiliary discharge device, and thus varying themagnitude of the charge which is to be applied to the capacitor toproduce excitation of the auxiliary discharge device. In the practice ofour invention, either of these elements is so varied that the frequencyof discharge of the main discharge device corresponds to the frequencyof movement of the body 9 under observation. This correspondence isattained by subjecting the body 9 to the illumination from the dischargedevice and by slowly varying the resistor or the control battery untilthe body appears to be at rest.

In the apparatus shown in Fig. 2, the proper periodicity of illuminationis attained by utilizing the output of a master oscillator 33, thefrequency of which may be varied. Here again, a capacitor I3 isconnected between the mercury pool 5 and the anode 3. of the maindischarge device I. The capacitor I3 is charged from a source 34 throughan auxiliary discharge device 35 of the type having an anode 31, acathode 39 and a control electrode 4|. If the source 34' utilized forcharging is of the alternating current type, the auxiliary dischargedevice 535 should preferably be of the asymmetric type and should be soconnected to the capacitor I3 that the capacitor plate 63 which isconnected to the anode 3 of the main discharge device I is chargedpositive.

The excitation of the auxiliary discharge device 35' is controlled. fromthe master oscillator 33. A potential provided by the master oscillator33 is impressed between the control electrode 4| and the cathode 39through a secondary section 45 of a suitable transformer 41 and thedischarge device 35 is energized at a frequency corresponding tothat ofthe master oscillator.

The master oscillator 33 also provides current impulses for energizingthe main discharge device. For this purpose, another secondary section 49 of the transformer 47 is connected between the starting electrode 'I-and the mercury pool 5- of the main discharge device I through asuitable rectifier 5I. Half-Wave impulses produced by the oscillator 33are thus transmitted through the starting electrode 7 of the maindischarge device I and periodically initiate the discharge in the maindischarge device, the anode-cathode potential being supplied by thecapacitor I3.

To provide for precise operation of the main discharge device I, thesecondaries 45 and 49 of the oscillator transformer 41 are so wound thatthe initiating discharge through the starting electrodes of the main.discharge device after the capacitor I3 has been charged and when theauxiliary discharge dea is only transmitted vice 35 blocks the chargingcurrent. Preferably, the potential supplied'to the control circuit oftheauxiliary discharge device 35 is m opposite phase to the potentialsupplied between the starting electrodes I and of-the main dischargedevice I, to accomplish this purpose.

The operation of the apparatus is illustrated in Fig. 3. In this view,the full-line sinecurve 53 representsthe control potential supplied bythe oscillator 33 to the auxiliary discharge device 35. The broken-linesine curve 55 represents the control potential supplied between thestarting electrodes 1 and 5. It will be noted that the fullline and thebroken-line curves 53 and 55 are in opposite phase. The potentialdifference impressed on the capacitor I3 is represented by the full-linecurve 51 rising above the sine curves. If the resistance in series withthe capacitor I3 is comparatively small, the capacitor may be chargedduring the interval corresponding to a single half-wave of the potentialsupplied by the oscillator 33 as illustrated. During the succeeding halfcycle, sufiicient current is transmitted between the starting electrode1 and the mercury pool 5 of the main discharge device to energize themain discharge device I and the main discharge device having beenenergized, the capacitor I3 is discharged.

A rectifier 59 is connected between the anode 3 and the cathode 5 of themain discharge device I to prevent the current in the main dischargedevice from oscillating. The cathode 6| of the rectifier 59 is connectedto the anode 3 of the main discharge device I and the anode 63 of therectifier is connected to the mercury pool 5. If there is a tendency tooscillate, the rectifier network absorbs the oscillations.

In the apparatus shown in Fig. 4, the capacitor I3 connected between theanode and the cathode of the main discharge device is charged during apredetermined interval of time and after it has been so charged, it isdischarged during a later interval of time.

For this purpose, an auxiliary discharge device 35 similar to thedischarge device utilized inthe modification shown in Fig. 2 is providedin series with the power source 34 and the capacitor |3. The cathode 39of the auxiliary discharge device 35 is connected to the plate 43 of thecapacitor l3 that is to be charged positive and the anode 3! isconnected to the source. Normally, the discharge device 35 is innon-conductive condition by reason of the functioning of a biasingbattery 55 connected between the cathode 39 and the control electrode 41which maintains the interval of time, the control electrode 4| is at thesame potential as the cathode 39. The discharge device, therefore,passes current to charge the capacitor l3. The total resistance inseries with the capacitor is comparatively low and the capacitor ischarged in a short interval of time.

To ignite the main discharge device I, a second commutator mounted onthe shaft 11 of the commutator 69 and rotating in synchronism isprovided. The second commutator I5 is provided 'with a conductingsegment 19 which iis directly connected 'to the starting electrode 1. Abrush 8| 'in'coritact with the surface of the commutator i5 isconnectedto that plate 43' of the capacitor |3 which is charged positive througha suitable impedance 83. The impedance properly regulates the startingimpulse of current when it'is transmitted,

Theconducting segment 19 on the last-mentioned commutator i5 isdisplaced in phase with respect to the conducting segment 1| of thefirstmentioned capacitor 59. It operates when contacted by its brush 8!to discharge the capacitor 3, after it'has been charged, through thestarting electrode! and the mercury pool 5. The charge on the capacitorI3 is not exhausted by the impulse transmitted through the startingelectrode 1' and the'residual difference of potential is of sufficientmagnitude to cause'the main discharge device! to become energized. Whenthe main discharge device is energized, the starting elec-} trodecircuit isshunted out. It will be seen from the above description that asmall portion of the 'chargeon the capacitor is utilized to ignite thedischargedevice after-which the residual charge is utilized in"producing the main discharge. A single-capacitor serves the doublefunction of providing starting current and discharge potential. Theperiodicity of the discharge produced in the main discharge device maybe varied by varying the speed of the commutators 59 and 15.

In the apparatus shown in Fig. 5, the capacitor |3 connected between theanode 3 and the oathode 5 of the main discharge device I is chargedthrough a half-wave rectifier from an alternating source 34. Todischarge the capacitor l3 through the starting electrode 1, anauxiliary discharge device 2|, similar to the discharge device utilizedin the embodiment shown in Fig. 1, is provided in series with thestarting electrode 1 and the cooperative mercury pool 5. The cathode '25of the auxiliary discharge device 2| is connected through the limitingresistor 29 to the starting electrode 1, and the anode 23 is connectedto the positive plate 93 of the capacitor l3.

The control circuit of the auxiliary discharge device 2| is suppliedfrom a transformer 81, the primary 99 of which is connected across thesecondary 9| of the main power supply transformer 93. However, theterminals of the primary 89 of the auxiliary transformer 81 are soarranged with respect to the terminals of the secondary 9| of the maintransformer 93 that the potential supplied in the control circuit of theauxiliary device 2| is displaced in phase with respect to the potentialsupplied by the secondary 9| of the main transformer.

In Fig. 6, the operation of the apparatus is illustrated graphically.The full-line sine curve 95 represents the potential supplied by themain transformer 93 and the broken-line sine curve 91 represents thecontrol potential supplied by the auxiliary transformer. Since theresistance in series with the capacitor l3 and the half-wave rectifier85 is small, the capacitor I3 is quickly charged during the half cyclesduring which the potential output of the main transformer 93 is suchthat rectifier B5 is conductive. The dot-dash curve 99 represents thecharging operation. After the capacitor |3 is charged and the chargingoperation is discontinued, the control potential supplied to theauxiliary discharge device 2| attains a value of sufficient magnitude toenergize the auxiliary discharge device. The capacitor |3 is thendischarged through the discharge device 2! and through the startingelectrode 1 of the main discharge device I'. The main discharge device Iis immediately energized under the influence of the residual potentialdifierence impressed on the capacitor and it remains energized until thecapacitor is discharged. After this, the capacitor is recharged and theprocess is repeated. It is to be noted that here again a singlecapacitor I3 is utilized for the double purpose of supplying startingcurrent and ignition potential.

Our invention has been herein shown and described as utilizing a maindischarge device I in which the cathode is a, mercury pool. Theprincipal advantage of such a discharge device resides in the intensecathode spot which forms on the surface of the cathode when thedischarge device is energized. Discharge devices having cathodes ofother types have been utilized by us and on the surface of the cathodein certain of these discharge devices a cathode spot also forms. We havefound this is particularly true of discharge devices in which thecathode is composed of such metals as cadmium, zinc, sodium, potassium,or alloys. of these metals. In the claim which follows, we shall referto a discharge device having a. mercury cathode or a mercury poolcathode.

We intend bythis expression to cover the general case of a cathode onwhich a cathode spot forms and the expression shall be taken to includecathodes of all types on which a cathode spot forms.

We claim as our invention;

An electrical system comprising a capacitor; means. for charging saidcapacitor, a discharge channel for said capacitor including anasymmetrically conductive main electric discharge device, said channelhaving a tendency to cause the current in said main discharge device tooscillate thereby to tend to produce back discharge of said capacitorthrough said discharge device; and unidirectional by-pass meansconnected in shunt with said discharge device in inverse conductivedirection thereto to prevent said current in said main discharge devicefrom oscillating.

DEWEY D. KNOWLES. CECIL E. HAILER.

REFERENCES CITED UNITED STATES PATENTS Name Date Rava Mar. 18, 1941Number

